Creating a negative from a positive .stl file

Hey everyone!

I found some mask files I want to use for some projects, my only problem is that they are 3d printing models with the texture on the outside. I am looking to carve these masks out of a block of plaster/silica material. The problem I'm having is all the texture is on the outside of the model, and I need that texture to be in the bottom of the cavity after I route the design.

I am not sure if I'm explaining this properly, but I essentially need a way to create a specific dimension block inside of autocad, and "extract" the mask from the block, leaving the design in the bottom of the block. I will then be filling this plaster/silica block with crushed glass in order to get all the texture of the mask on the outer facing side (once I remove the glass from the mold).

If anyone can help me, or explain to me how to accomplish this, I would appreciate it!

Best Wishes

That's called a boolean action, subtracting one solid from another

https://www.youtube.com/watch?v=Djh7ZSxuYYQ

HI, I sent you a PM

I'm not sure you really want to be carving that plaster-silica material. It will make a big mess, with toxic dust all over the place, and the abrasive silica won't be good for your CNC machine either. I'd suggest you carve the masks as positive forms (the way they come) in machinable wax (or 3D print them), build a wall around them out of clay, pour in the plaster-silica mixture, letting it set up before you remove the clay and the positive form. Aside from saving your machine and your health, doing it this way will also allow you to make as many of these molds as you want from the same model.

Andrew Werby
Juxtamorph.com

In sketchup, creating a negative from a positive takes like 30 seconds.

Import the STL. Draw a 3d box that completely incorporates the object. Click "Intersect faces with model". And you're done. Then you can split and manipulate your mold as needed.

As above said, it's always good practice to create negatives from reusable master molds.